Image resolution

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Image resolution is the level of detail of an image. The term applies to digital images, film images, and other types of images. "Higher resolution" means more image detail. Image resolution can be measured in various ways. Resolution quantifies how close lines can be to each other and still be visibly resolved. Resolution units can be tied to physical sizes (e.g. lines per mm, lines per inch), to the overall size of a picture (lines per picture height, also known simply as lines, TV lines, or TVL), or to angular subtense. Instead of single lines, line pairs are often used, composed of a dark line and an adjacent light line; for example, a resolution of 10 lines per millimeter means 5 dark lines alternating with 5 light lines, or 5 line pairs per millimeter (5 LP/mm). Photographic lens are most often quoted in line pairs per millimeter.

Contents

Types

The resolution of digital cameras can be described in many different ways.

Pixel count

The term resolution is often considered equivalent to pixel count in digital imaging, though international standards in the digital camera field specify it should instead be called "Number of Total Pixels" in relation to image sensors, and as "Number of Recorded Pixels" for what is fully captured. Hence, CIPA DCG-001 calls for notation such as "Number of Recorded Pixels 1000 × 1500". [1] [2] According to the same standards, the "Number of Effective Pixels" that an image sensor or digital camera has is the count of pixel sensors that contribute to the final image (including pixels not in said image but nevertheless support the image filtering process), as opposed to the number of total pixels, which includes unused or light-shielded pixels around the edges.

An image of N pixels height by M pixels wide can have any resolution less than N lines per picture height, or N TV lines. But when the pixel counts are referred to as "resolution", the convention is to describe the pixel resolution with the set of two positive integer numbers, where the first number is the number of pixel columns (width) and the second is the number of pixel rows (height), for example as 7680 × 6876. Another popular convention is to cite resolution as the total number of pixels in the image, typically given as number of megapixels, which can be calculated by multiplying pixel columns by pixel rows and dividing by one million. Other conventions include describing pixels per length unit or pixels per area unit, such as pixels per inch or per square inch. None of these pixel resolutions are true resolutions[ clarification needed ], but they are widely referred to as such; they serve as upper bounds on image resolution.

Below is an illustration of how the same image might appear at different pixel resolutions, if the pixels were poorly rendered as sharp squares (normally, a smooth image reconstruction from pixels would be preferred, but for illustration of pixels, the sharp squares make the point better).

Resolution illustration.png

An image that is 2048 pixels in width and 1536 pixels in height has a total of 2048×1536 = 3,145,728 pixels or 3.1 megapixels. One could refer to it as 2048 by 1536 or a 3.1-megapixel image. The image would be a very low quality image (72ppi) if printed at about 28.5 inches wide, but a very good quality (300ppi) image if printed at about 7 inches wide.

The number of photodiodes in a color digital camera image sensor is often a multiple of the number of pixels in the image it produces, because information from an array of color image sensors is used to reconstruct the color of a single pixel. The image has to be interpolated or demosaiced to produce all three colors for each output pixel.

Spatial resolution

The terms blurriness and sharpness are used for digital images but other descriptors are used to reference the hardware capturing and displaying the images.

Spatial resolution in radiology is the ability of the imaging modality to differentiate two objects. Low spatial resolution techniques will be unable to differentiate between two objects that are relatively close together.

The 1951 USAF resolution test target is a classic test target used to determine spatial resolution of imaging sensors and imaging systems. 1951usaf test target.jpg
The 1951 USAF resolution test target is a classic test target used to determine spatial resolution of imaging sensors and imaging systems.
Matakis - blurred.jpg
MARTAKIS1.jpg
Image at left has a higher pixel count than the one to the right, but is still of worse spatial resolution.

The measure of how closely lines can be resolved in an image is called spatial resolution, and it depends on properties of the system creating the image, not just the pixel resolution in pixels per inch (ppi). For practical purposes the clarity of the image is decided by its spatial resolution, not the number of pixels in an image. In effect, spatial resolution is the number of independent pixel values per unit length.

The spatial resolution of consumer displays ranges from 50 to 800 pixel lines per inch. With scanners, optical resolution is sometimes used to distinguish spatial resolution from the number of pixels per inch.

In remote sensing, spatial resolution is typically limited by diffraction, as well as by aberrations, imperfect focus, and atmospheric distortion. The ground sample distance (GSD) of an image, the pixel spacing on the Earth's surface, is typically considerably smaller than the resolvable spot size.

In astronomy, one often measures spatial resolution in data points per arcsecond subtended at the point of observation, because the physical distance between objects in the image depends on their distance away and this varies widely with the object of interest. On the other hand, in electron microscopy, line or fringe resolution is the minimum separation detectable between adjacent parallel lines (e.g. between planes of atoms), whereas point resolution is instead the minimum separation between adjacent points that can be both detected and interpreted e.g. as adjacent columns of atoms, for instance. The former often helps one detect periodicity in specimens, whereas the latter (although more difficult to achieve) is key to visualizing how individual atoms interact.

In Stereoscopic 3D images, spatial resolution could be defined as the spatial information recorded or captured by two viewpoints of a stereo camera (left and right camera).

Spectral resolution

Pixel encoding limits the information stored in a digital image, and the term color profile is used for digital images but other descriptors are used to reference the hardware capturing and displaying the images.

Spectral resolution is the ability to resolve spectral features and bands into their separate components. Color images distinguish light of different spectra. Multispectral images can resolve even finer differences of spectrum or wavelength by measuring and storing more than the traditional 3 of common RGB color images.

Temporal resolution

Temporal resolution (TR) is the precision of a measurement with respect to time.

Movie cameras and high-speed cameras can resolve events at different points in time. The time resolution used for movies is usually 24 to 48 frames per second (frames/s), whereas high-speed cameras may resolve 50 to 300 frames/s, or even more.

The Heisenberg uncertainty principle describes the fundamental limit on the maximum spatial resolution of information about a particle's coordinates imposed by the measurement or existence of information regarding its momentum to any degree of precision.

This fundamental limitation can, in turn, be a factor in the maximum imaging resolution at subatomic scales, as can be encountered using scanning electron microscopes.

Radiometric resolution

Radiometric resolution determines how finely a system can represent or distinguish differences of intensity, and is usually expressed as a number of levels or a number of bits, for example 8 bits or 256 levels that is typical of computer image files. The higher the radiometric resolution, the better subtle differences of intensity or reflectivity can be represented, at least in theory. In practice, the effective radiometric resolution is typically limited by the noise level, rather than by the number of bits of representation.

Resolution in various media

This is a list of traditional, analogue horizontal resolutions for various media. The list only includes popular formats, not rare formats, and all values are approximate, because the actual quality can vary machine-to-machine or tape-to-tape. For ease-of-comparison, all values are for the NTSC system. (For PAL systems, replace 480 with 576.) Analog formats usually had less chroma resolution.

Many cameras and displays offset the color components relative to each other or mix up temporal with spatial resolution:

PPIPixelsmm
800100031.8
300100084.7
2001000127
721000352.8
PPIPixelsmm
8003150100
3001181100
200787100
72283100
PPIPixelsmm Paper size
3009921×14008840×1186A0
3007016×9921594×840A1
3004961×7016420×594A2
3003508×4961297×420A3
3002480×3508210×297A4
3001748×2480148×210A5
3001240×1748105×148A6
300874×124074×105A7
300614×87452×74A8

See also

Related Research Articles

<span class="mw-page-title-main">Digital video</span> Digital electronic representation of moving visual images

Digital video is an electronic representation of moving visual images (video) in the form of encoded digital data. This is in contrast to analog video, which represents moving visual images in the form of analog signals. Digital video comprises a series of digital images displayed in rapid succession, usually at 24, 30, or 60 frames per second. Digital video has many advantages such as easy copying, multicasting, sharing and storage.

<span class="mw-page-title-main">Pixel</span> Physical point in a raster image

In digital imaging, a pixel, pel, or picture element is the smallest addressable element in a raster image, or the smallest addressable element in a dot matrix display device. In most digital display devices, pixels are the smallest element that can be manipulated through software.

<span class="mw-page-title-main">Standard-definition television</span> Digital television with a similar definition to legacy analog systems

Standard-definition television is a television system that uses a resolution that is not considered to be either high or enhanced definition. Standard refers to offering a similar resolution to the analog broadcast systems used when it was introduced.

<span class="mw-page-title-main">Video</span> Electronic moving image

Video is an electronic medium for the recording, copying, playback, broadcasting, and display of moving visual media. Video was first developed for mechanical television systems, which were quickly replaced by cathode-ray tube (CRT) systems, which, in turn, were replaced by flat-panel displays of several types.

<span class="mw-page-title-main">Chroma subsampling</span> Practice of encoding images

Chroma subsampling is the practice of encoding images by implementing less resolution for chroma information than for luma information, taking advantage of the human visual system's lower acuity for color differences than for luminance.

<span class="mw-page-title-main">D-1 (Sony)</span> Magnetic tape-based videocassette format

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<span class="mw-page-title-main">Display resolution</span> Number of distinct pixels in each dimension that can be displayed

The display resolution or display modes of a digital television, computer monitor or display device is the number of distinct pixels in each dimension that can be displayed. It can be an ambiguous term especially as the displayed resolution is controlled by different factors in cathode ray tube (CRT) displays, flat-panel displays and projection displays using fixed picture-element (pixel) arrays.

<span class="mw-page-title-main">480i</span> Standard-definition video mode

480i is the video mode used for standard-definition digital video in the Caribbean, Japan, South Korea, Taiwan, Philippines, Myanmar, Western Sahara, and most of the Americas. The other common standard definition digital standard, used in the rest of the world, is 576i.

<span class="mw-page-title-main">576i</span> Standard-definition video mode

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High-definition video is video of higher resolution and quality than standard-definition. While there is no standardized meaning for high-definition, generally any video image with considerably more than 480 vertical scan lines or 576 vertical lines (Europe) is considered high-definition. 480 scan lines is generally the minimum even though the majority of systems greatly exceed that. Images of standard resolution captured at rates faster than normal, by a high-speed camera may be considered high-definition in some contexts. Some television series shot on high-definition video are made to look as if they have been shot on film, a technique which is often known as filmizing.

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<span class="mw-page-title-main">Pixel aspect ratio</span> Proportion between the width and the height of a pixel

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<span class="mw-page-title-main">Sony camcorders</span>

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The Sony DCR-VX1000 was a DV tape camcorder released by Sony in 1995. A VX1000 was used to film the British hidden camera show Trigger Happy TV. It was also used by many skateboarders in the late 90s and early 2000s and therefore is an important part in the history of skateboarding culture. The VX1000 was based on Sony's earlier VX1 (PAL) and VX3 (NTSC) Hi8 camcorders, which were similarly intended as "prosumer" models, targeted at both high-end consumer and low-end professional users. In the mid-1990s, Sony began to move away from Hi8 tape in favor of the emerging DV format, and as a result the VX3 and VX1 were discontinued in 1995. However, their iconic form factor, with a distinctively-shaped stereo microphone array at the front of the handle, was reused by the VX1000 and numerous later Sony DV and HDV camcorders in the VX, PD, FX and Z lines.

<span class="mw-page-title-main">Canon EOS 50D</span> DSLR camera

The Canon EOS 50D is a 15.1-megapixel digital single-lens reflex camera. It is part of the Canon EOS line of cameras, succeeding the EOS 40D and preceding the EOS 60D.

<span class="mw-page-title-main">Graphics display resolution</span> Width and height of an electronic visual display device, such as a computer monitor, in pixels

The graphics display resolution is the width and height dimension of an electronic visual display device, measured in pixels. This information is used for electronic devices such as a computer monitor. Certain combinations of width and height are standardized and typically given a name and an initialism which is descriptive of its dimensions. A graphics display resolution can be used in tandem with the size of the graphics display to calculate pixel density. An increase in the pixel density often correlates with a decrease in the size of individual pixels on a display.

References

  1. ↑ Archived 2017-02-02 at the Wayback Machine Guideline for Noting Digital Camera Specifications in Catalogs. "The term 'Resolution' shall not be used for the number of recorded pixels"
  2. ↑ ANSI/I3A IT10.7000–2004 Photography – Digital Still Cameras – Guidelines for Reporting Pixel-Related Specifications
  3. ↑ "Video resolution comparison chart".
  4. ↑ "Kodak VISION3 500T Color Negative Film 5219 / 7219 / SO-219" (PDF). July 2015.
  5. ↑ An analysis of film resolution
  6. ↑ Understanding image sharpness part 1A: Resolution and MTF curves in film and lenses, by Norman Koren
  7. ↑ "/Film Interview: IMAX Executives Talk 'The Hunger Games: Catching Fire' and IMAX Misconceptions". Slash Film. December 2, 2013. Retrieved December 17, 2013.
  8. ↑ "Phaseone". Archived from the original on 2012-03-18.
  9. ↑ "Leaf Aptus Medium Format Digital Backs". www.mamiyaleaf.com. Archived from the original on 2015-09-24. Retrieved 2013-11-06.
  10. ↑ DxO. "Phase One IQ180 Digital Back: Tests and Reviews – DxOMark". www.dxomark.com.
  11. ↑ Forret, Peter. "Megapixel calculator – toolstudio". web.forret.com.
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